(
SELECT 1 AS sort_col, products.*,
IF(products.url_custom='',products.url_default,products.url_custom) AS product_url,
catalog.name AS cat_name,
IF(catalog.url_custom='',catalog.url_default,catalog.url_custom) AS cat_url,
manufacturer_name
FROM products
INNER JOIN products_categories ON products_categories.pid = products.pid AND ( products_categories.cid='42' OR products_categories.cid='176' OR products_categories.cid='229' OR products_categories.cid='213' OR products_categories.cid='146' OR products_categories.cid='148' OR products_categories.cid='255' OR products_categories.cid='147' OR products_categories.cid='153' OR products_categories.cid='162' OR products_categories.cid='150' OR products_categories.cid='259' OR products_categories.cid='149' )
INNER JOIN catalog ON products.cid=catalog.cid
LEFT JOIN manufacturers ON manufacturers.is_visible='1' AND products.manufacturer_id = manufacturers.manufacturer_id
WHERE products.is_visible='Yes'

AND products.call_for_price = 'No' AND products.stock > 0
GROUP BY products.pid
ORDER BY products.price, products.title
)
UNION
(
SELECT 2, products.*,
IF(products.url_custom='',products.url_default,products.url_custom) AS product_url,
catalog.name AS cat_name,
IF(catalog.url_custom='',catalog.url_default,catalog.url_custom) AS cat_url,
manufacturer_name
FROM products
INNER JOIN products_categories ON products_categories.pid = products.pid AND ( products_categories.cid='42' OR products_categories.cid='176' OR products_categories.cid='229' OR products_categories.cid='213' OR products_categories.cid='146' OR products_categories.cid='148' OR products_categories.cid='255' OR products_categories.cid='147' OR products_categories.cid='153' OR products_categories.cid='162' OR products_categories.cid='150' OR products_categories.cid='259' OR products_categories.cid='149' )
INNER JOIN catalog ON products.cid=catalog.cid
LEFT JOIN manufacturers ON manufacturers.is_visible='1' AND products.manufacturer_id = manufacturers.manufacturer_id
WHERE products.is_visible='Yes'

AND (products.call_for_price = 'Yes' OR products.stock = 0)
GROUP BY products.pid
ORDER BY products.price, products.title
)

ORDER BY sort_col,
LIMIT 20, 10

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'LIMIT 20, 10' at line 36